The present invention pertains to mixing apparatus for concrete and other materials and, more particularly, to an assembly for demountably and adjustably mounting the mixing blades in a rotary pantype mixer.
Pan mixers are well known in the art and are used to batch mix a wide variety of materials, including concrete, glass, foundry sand, and a variety of industrial by-products such as fly ash. Pan-type mixers typically utilize a shallow annular mixing chamber having a flat bottom and concentric outer and inner cylindrical side walls. The cylindrical inner side wall houses an appropriate rotary drive system which typically drives a variety of mixing and blending tools which depend downwardly into the mixing chamber for rotational movement therein. Because many of the materials which are mixed in a pan-mixer are highly abrasive, the rotational mixing, blending, and scraping tools are subject to extreme wear, even when made of wear-resistant metals. Thus, the positions of the tools must be periodically adjusted to maintain proper positioning with respect to the walls of the mixing chamber to compensate for wear and, further, must be demountable for replacement when excessive wear has occurred.
U.S. Pat. No. 4,506,984 shows a prior art pan-type mixer, including an assembly for demountably and adjustably attaching the main mixing paddles or blades for rotational movement in the mixing chamber over and closely spaced from the chamber bottom wall. This prior art paddle mounting assembly includes a downwardly depending paddle mounting arm having a bracket at its lower end to which the paddle is demountably attached. The attachment assembly includes a connector plate which slides in a T-shaped slot in the back of the paddle and has a pair of threaded studs extending out of the paddle slot and through a slotted mounting bracket to provide interim vertical adjustment of the paddle, as well as eventual removal for replacement. Another prior art arrangement utilizes a pair of mounting bolts which extend through the front face of the paddle with the bolt heads recessed in the paddle face and the opposite threaded ends extending through a mounting bracket and secured thereto with conventional nuts and lock washers.
In both of the foregoing prior art mounting assemblies, the mounting bolt pairs have threaded ends which are exposed to the abrasive action of the materials being mixed. In the latter prior art arrangement, the bolt heads are also exposed to abrasive action. In addition, when mixing materials such as concrete, cement typically builds up on all exposed surfaces, including the exposed threaded bolt ends, connecting nuts and bolt heads of the various prior art assemblies. As a result, the threaded connections become difficult or impossible to loosen and, when subjected to abrasive action for extended periods, may even wear to the point of failure.
Attempts have been made in the prior art to attach the paddle mounting arm with a vertically adjustable connection at its upper end above the normal level of material being mixed so that the paddle height is adjusted by vertical adjustment of the arm to which it is attached. However, these mounting assemblies have typically utilized two bolts or similar threaded connectors and complex adjustment mechanisms which are subject to infiltration by airborne cement and other dust which accumulates and cakes on the connectors and adjustment mechanism. One such adjustment mechanism is also shown in the above identified patent.
There is a need, therefore, for a simple paddle or blade mounting system for rotary pan-type mixers which is well protected from the abrasive action of materials being mixed, better sealed against infiltration of airborne cement fines and other dust particles, and is simple to adjust and disassemble for replacement.